Embodiments described herein relate to clot detection in a pipetting apparatus, and more particularly relate to the detection of clot caused when substance in a liquid sample is adhered to a tip portion of a sampling nozzle, for instance.
In testing of a sample, it is desirable to perform pipetting operation which obtains any required volume of the sample by aspiration. In general, the pipetting operation is carried out by inserting a nozzle connected to a suction pump into the sample contained in a test tube or the like to aspirate and obtain a required volume of the sample. As an apparatus for performing the pipetting operation, a pipetting apparatus is well known.
Recently, in particular, an automatic pipetting apparatus has been widely used, in which the respective pipetting processes can be carried out automatically and continuously without assistance of an operator.
In the automatic pipetting apparatus as described above, the constituents of blood such as serum or plasma collected from a living body is often used as a sample to be pipetted. The pipetted sample is mixed with a chemical reagent or others to carry out a predetermined test.
The blood serum or plasma is obtained from blood by a centrifugal separation, and in many cases thus obtained serum or plasma is used as it is for the sample. When thus obtained blood sample is pipetted, there is a problem in that the tip portion of the nozzle is likely to be clotted with foreign matters such as solid substance or fibrous substance contained in the sample or a serum separating medium, thus resulting in a clotting condition. When the pipetting operation is carried out under the clotting condition, there arises a problem in that the accuracy of pipetting is deteriorated.
In view of this problem, a method for detecting clot caused in an automatic pipetting apparatus has been proposed in Japanese Laid-open Patent Publication No. 2184762. In this conventional method, the pressure within the nozzle is detected by a pressure sensor. Changes in pressure detected by the pressure sensor are monitored. The clotting condition can be detected when waveform indicating the pressure changes shifts to a negative value side abruptly. In more detail, the pressure is sampled for each predetermined period, and the difference between the current detected pressure and the preceding detected pressure is compared with a threshold value to discriminate the clotting condition.
In the conventional pipetting apparatus, however, the sampling period is set short in order to detect the clotting condition as soon as possible, and further since the threshold value is determined so as to correspond to the short sampling period. For this reason, there is a problem in that it is difficult to detect an imperfect clotting condition, because under the imperfect clotting condition the pressure change is so small as not to be detectable by this detecting method of the conventional pipetting apparatus. Therefore, in the conventional apparatus, there is a problem that, when the pipetting accuracy is deteriorated due to such imperfect clotting condition, it has been difficult to detect such undesirable condition.
In order to overcome the above-mentioned problems, it is desirable to provide an automatic pipetting apparatus which can detect imperfect clotting conditions as well as perfect clotting condition.